Fail-safe control system



United States Patent 3,252,141 FAIL-SAFE CONTROL SYSTEM Leo L. Galin, Chicago, Ill., assignor, by mesne assignments, to Omnitronie Corporation, Richmond, Ind., a corporation of Illinois Filed July 31, 1961, Ser. No. 128,130 24 Claims. (Cl. 340-164) This invention relates to a system, and to the control circuit thereof, for operating a device such as a warning or like device in accordance with the presence or absence of spaced recurrent control signals.

The control circuit and system has utility in many different fields, but for convenience it is described below in relation to a railroad track gang warning system, no limitation thereto being intended.

In many sections of railroad all over the world, there are dual tracks set side by side over which trains proceed in opposite directions. These sets of tracks are usually quite close to one another, so close in fact that when a gang of workmen is repairing one of the tracks, some of the workmen may be on the other track in danger of any train approaching thereon. It is one of the purposes of this invention to providev a warning system which will be fail-safe in its warning of railroad workmen that a train is approachingtheir area of work.

In a specific embodiment, some sort of warning device,

preferably of the audible type (such as a born or audio oscillator of the siren type) though it may be visual if desired, is located within sensing range of each of the workmen. Connected to this device, of which there actually may be several in the Work area so connected, is

a special control circuit that operates to keep the Warning device inoperable as long as certain spaced recurrent control signals are received frequently enough. These control signals are preferably two dilferent frequency bursts of signal, or tones, that are transmitted alternately by means of a transmitter located at a watchmans station disposed an appropriate distance from the work gang. When the watchman sees a train approaching, he verifies its position and speed optically and when it approximates a designateddistance from the gang of workmen, the watchman opens a transmitter circuit and holds it open until the train has passed. The opening of the transmitter circuit prevents any radio frequency or tones that are modulated thereon at the transmitter from being transmitted during the period that circuit is open. However, upon subsequent closing of the transmitter circuit, the transmission consists of control tones alternately 'modu lated at spaced times onto a radio frequency carrier signal, which itself is preferably not transmitted between the times when neither tone is modulated thereon. At the location of the workmen, there is a superheterodyne receiver or the like which demodulates the control tones and presents them to the control circuit; As long as the control tones are recurrently and periodically received, the warning device is held inoperative. However, if either or both of the control tones does not recur often enough, as is the situation when the watchman opens the transmitter circuit, the part of the control circuit that keeps the warning device inoperative acts to'energize the warning device.

There are many prior art systems of this general nature, i.e., of the type that energize warning devices or the like,

but these operate in response to the presence of control signals, rather than the absence of such as does this invention. For this reason, the systems-of the priorart are not fail-safe to the extent that is apparatus built in accordance with this invention. That is, since the warning device herein is operated when tones fail to be received, there is less chance of the warning device not being operated when something goes wrong with the system, than is the 'case with prior art systems. For example, if the energy supply at the transmitter becomes weak or goes dead, the transmitter will not transmit either of the control tones nor an RF signal, thereby causing a warning signal at the receiver end. This immediately notifies the watchman that something is wrong at the transmitter, for example that a battery needs replacing.

However, with the prior art type of devices, a battery can become sufiiciently weak to prevent the desired transmission when needed, but the watchman may not be apprised of this ahead of time, but only at a time too late for the full safety of the workmen.

It is therefore, one of the main purposes of this invention to provide a novel fail-safe warning system.

Other objects and advantages of this invention will become apparent to those of ordinary skill in the art after reading this specification and appended claims in conjunction with the drawing, in which:

FIGURE 1 illustrates a transmitter constructed in ac: cordance with this invention, and

FIGURE 2 illustrates a receiver including a control circuit for controlling a warning device.

In FIGURE 1, block 10 represents a radio frequency transmitter and its power source. The power source may be of any type desired, but since the specific description herein relates to use of the transmitter in the field, it is presumed that the power source is of the battery type. As exemplary, without limitation being intended, the radio frequency (RF) carrier generated. and transmitted over antenna 12 while the watchmans push button switch 14 is closed, may have a frequency of 27.255 me. As shown for convenience, switch 14 is in the antenna circuit, but it may be located in any other desired circuit in the transmitting system as long as it can effect its main purpose of preventing transmission of at least the control signals if not also the RF carrier.

For purpose of conserving battery power, it is preferable to interrupt the generation of the RF signal periodically, i.e., to pulse the carrier signal on and off every so often, for example on for 0.25second every 0.5 second, though the carrier signal may be left on continuously if so desired. In the latter event, it is then only necessary to generate the two different frequency tones and alternately impose them at spaced times on the RF signal. However, if the RF signal is itself pulsed on and off also, then its on times must be synchronized with the on times of the tones. FIGURE 1 illustrates apparatus for effecting such synchronization.

The two control tones, respectively designated A and B, and which may respectively have a frequency of 1,000 c.p.s. and 2,400 c.p.s., are produced in generators 16 and 18 upon delivery thereto of energy via the power line 20. With such an arrangement, the tone signals are present on their respective output lines 22 and 24 continuously, though the energy over line 20 may be pulsed alternately to generators 16 and 18 to provide alternate tone outputs on lines 22 and 24, if desired to save further battery power. However, any re-start inertia of generators 16 and 18 need not be continually overcome, and more accuracy in the frequency of tones A and B may be effected by continuous generation of those tones, which then may subsequently 'be modulated alternately onto the RF signal, in the exemplary manner now to be described. I Motor 26 is operated by power via line 28, and it rotates cams 30 and 32 in unison in the direction indicated, each of these cams having respective cam surfaces 34 and 36 oriented approximately 180 apart. When cam surface 36 rotates underneath the switch actuating element 38, both its switches 40 and 42 are closed. Soon after these switches are reopened, cam surface 34 comes under switch actuating element 44 which in turn causes switches 46 and 48 to close for a short time. It will be noted that switches 48 and 42 are connected in parallel by lines 50 and 52, whereby the power on line 54 for generating the RF signal in the transmitter is conveyed .back into the transmitter via' line 56 when either of switches 42 or 48 is closed. However, switches 40 and 46 are not connected together, but respectively convey tones B and A into the transmitter via lines 58 and 60. In this manner, when cam surface 34 is operative to actuate its switches, tone A is applied to the transmitter for modulation onto the RF signal then generated, but tone B is not mixed therewith. On the other hand, when cam surface 36 operates its switches, tone A is not ap-.

plied to the transmitter, but tone B is for modulation onto the RF signal then being generated.

Any other desired type of mechanical, electrical, magnetic or electronic switching may be employed to effect alternate generation of or modulation by the tones and, if desired, interruption of carrier generation. Modulation in the transmitter of the tones with the RF signal may be of any type desired, amplitude or frequency modulation for example, and in any event, it is apparent that antenna 12 will transmit an RF signal for a given time with tone A modulated thereon, followed by a space of no transmission of either the RF or tones, followed in turn by the carrier modulated with tone B for another short time, with the fourth period of time in the cycle being again no transmission of either the carrier or tones.

This cycling may be interrupted 'when the watchman notices that an approaching train has reached a proximity close enough to warn workers of its approach.

The radiated signal, when not so interrupted, is received in FIGURE 2 by antenna and applied to the superheterodyne receiver 72 for demodulation purposes so that tones A and B occur on output line 74, which is the input line to the control circuit schematically illustrated in detail. This control circuit preferably involves two parallel channels 76 and 76, which are exactly alike except for the frequency characteristic of their respective tone rejecting or discrimination means such as the parallel LC, narrow 'band elimination filters 78 and 80. Both channels are connected to the same input line 74, and to the same output line 82 with which is associated at least one warning device 84, which, as previously indicated, is preferably of the audio type such as a horn or siren.

Since channels 76 and 76' are similar, only one is herein described in detail, with corresponding parts of the other being designated with a .like number primed, it being necessary to remember that one channel, channel 76, operates relative to tone A, while channel 76 operates relative to tone B. For effecting such operation, filters 78 and may have a selectivity of approximately :30%, for example.

Filter 78 in channel 76 presents a high impedance to only those signals which have a frequency of approximately that of tone A, for example 1,000 c.p.s. Therefore, each received control signal of this frequency is coupled to the base 86 of transistor 88 via the series combination of condenser 90 and limiting resistor 92, instead of to a common potential point (such as ground) via therethrough to decrease to 2 ma.

ditions and energize the Warning device.

filter 78 and diode 94 as is the path for other frequencies which filter 78 willpass. Tone A as thereby received by transistor 88 causes that transistor to change from a non-conductive state, to which it is normally biased by the exemplary supply potential of -12 volts at terminal 96 and voltage dividing resistor 98 and 100 in conjunction with emitter resistor 102, to a conductive state once for each negative half cycle of the tone A burst. Accordingly, with collector 104 being coupled to the supply votlage via resistor 106, the emitter junction 108 supplies a plurality of negative-going signals during each burst of tone received by transistor 88. These pulses are smoothed by condenser 110 and applied to the base 112 of transistor 114, thereby making this transistor conductive during the whole of each received control tone.

Transistor 114 is connected as an amplifier with coil 116 of a multi-condition switching means such as relay 118 being in its collector circuit. Collector 126 is also connected at junction 120 to a condenser 122 which is otherwise connected to ground. While transistor 114 is conductive, conventional current flows from ground through emitter 124, collector 126, and relay coil 116 to supply terminal 96. With relay coil 116 having a resistance of approximately 3,000 ohms for example, at least about 3 milliamperes (ma) flows therethrough when transistor 114 is conductive. This is sufficient to energize relay 118 so that its armature 128 is held upwardly against contact 130. When a control tone ceases, however, though transistor'114 cuts off, relay 118 is not immediately de-energized but condenser 122 begins charging towards the supply voltage, i.e., toward l2 volts. Before cut off of transistor 114, junction 120 is no more negative than about 3 volts with respect to ground, if that much. Upon cessation of tone A, relay armature 128 does not immediately drop down onto contact 132, and does not do so at all unless condenser 122 has time enough to charge up to a predetermined voltage, for example 6 volts negative. That is, if the period between successive tones of 1,000 c.p.s. is too long, condenser 122 charges at least to 6 volts, which in turn decreases the voltage across relay coil 116, causing the current drops down against contact 132, which is connected at terminal 134 to a source of energization, AC. or DC. as desired, to complete a path via lines 136 and 82 for energizing warning device 84. Since the multi-condition relay armatures 128 and 128' are connected in common or together by lines 136 and 136' to line 82 and the warning device, cessation of either tone for too long a time will effect a signalling indication such as a warning from device 84.

Accordingly, as long as the 1,000 c.p.s. A tones and 2,400 c.p.s. B tones both occur often enough to prevent the respective condensers 122 and 122' from being charged up to. the exemplary 6 volts, neither of the relay armatures 128 or 128' will be allowed to change from their normally unstable position in which they bear against contacts 130 and 130 to their respective normally stable condition in which they bear against contacts 132 and 132', thereby preventing actuation of the warning device 84. However, if the transmitter operator opens switch 14 in FIGURE 1, neither of the A or B tones will the received by the apparatus in FIGURE 2 for the period of time during which that switch is open, which time is sufficient to allow condensers 122' and 122' to charge sufficiently to de-energize the respective relays and allow their armatures to relax to their stable con- The number of tone pulses which need to be deleted by the operator upon opening switch 14 to effect actuation of the warning device, can be as desired, according to the time element related to the timing means includingcondensers 122 and 122. Their charge time can be short enough to effect de-energization of the relaysif only one A or B tone is prevented from being transmitted, if that type Armature 128 then ofoperation is desired, or on the other hand, the time resistance of the relay coils may be longer so that it requires more than one of the A and B tones to be absent before the warning device will be actuated.

Condenser 138 in channel 76 and condenser 138' in channel 76' are preferably present to feedback a partially regenerative signal to the junction between the respective filter and diode combinations, to give'added gain and selectivity to thecontrol circuit. If these condensers are not employed, diodes 94 and 94' need not be utilized.

Instead of LC filters 78 and 80, any other means for rejecting certain frequencies, such as vibrating reeds, may be employed, if desired.

Switch 14 in FIGURE 1 may be of the push button type which is spring-loaded closed so that the watchman must depress the button and hold it down to interrupt transmission while a train approaches and passes. On the other hand, switch 14 is preferably of the springloaded open type which needs to be held closed continuously until an approaching train is noted and it is necessary to stop transmission. With this latter type arrangement, the system becomes still more fail-safe in that provision is thereby made to warn the workmen of inadequacy on the part of the watchman to attend to their safety, a provision of the type frequently referred to as dead-man control.

Though the system has been above described relative to manual operation of the transmitter switch 14, such can be automatically operated in any desirable manner, for example by detection of the approach of a train by a sensing device of any desired sort located near the track perhaps a quarter mile away from the work gang. M-agnetic. field disturbance, heat sensitivity, or photoelectric interruption are a few of the numerous ways in which a detecting device may operate to sense an approaching train. Further, whatever the type of detecting mechanism, it may be mounted along with the transmitter on a remotely controlled buggy riding on the same track as the work gang but kept at a proper distance from the gang as the gang progresses :along the track. Such a buggy is described in the copending application of Brice E. Hayes, Serial No. 784,153, filed December 31, 1958, now Patent No. 3,000,099. Use of such a buggy would of course eliminate the necessity of a man as watchman. If desired, two such buggies, one each way from the gang, may be employed, so that traffic from both directions may be detected. In such a case, or when no such .Ibuggies but two watchman stations are so deployed, re-

spective transmitters operating on different sets of frequencies into respective receivers at the work gang location, or synchronized transmitters operating on the same frequencies into the same receiver, may be employed.

In FIGURE 2, it may be noted that relay contacts 130 and 130' are electrically'disconnected from each other or any other partof the circuitry. However, if desired, these two contacts may be connected together, and further, to ground, in which case both armatures 12-8 and 128' must relax to their stable condition in which they respectively bear against contacts 132 and 132', in order to release line 82 from ground potential. The advantage of contacts 130 and 130' not .being so connected is that if only one of the tones ceases to recur, a warning signal is nevertheless given to indicate failure of [a part of the circuitry at the transmitteror in the associated channel of the control circuit at the receiver. This failure.

The subject matter of this application is at least in part 6 application, Serial No. 251,662, filed January 15, 1963, which is assigned to the same assignee as the present application.

Thus it is apparent that the various objects and advantages herein set forth are successfully achieved. Modifications of this invention not described herein will become apparent to those of ordinary skill in the art after reading this disclosure. Therefore, it is intended that the matter contained in the foregoing disclosure and accompanying drawings be interpreted as illustrative, not limitative, the scope of the invention being defined in the appended claims.

What is claimed is:

' 1. "A control circuit for controlling a device in accordance with the presence or absence of different frequency, normally recurrent, control signals comprising:

a plurality of parallel channels having a common input for receiving all said control signals,

each channel being assigned adifferent one of said control signal frequencies and including frequency rejection means for passing, as between said control signals, only the one the frequency of which is assigned to the respective channel,

a plurality of timing means respectively coupled to the output of each said frequency rejection means of each channel for timing any interval of abnormal absence of any of said control signals and providing a plurality of predetermined output signals respectively in all of said channels only when said common input receives all of said different frequency control signals normally recurren-tly as aforesaid in satisfaction of the timing requirements of said timing means, and

a plurality of multi-condition means respectively responsive to said predetermined output signals to respectively effect in any one of said multi-condition means for the duration of the respective output signal a first operating condition for preventing operation of said device only during said first condition whereby cessation of any one or more of said control signals for a time exceeding said timing requirements of respectively any one or more of said timing means causes said multi-condition means to change to a second condition at least temporarily for causing operation of said device only during said second condition.

2. A fail-safe control circuit for controlling a device in accordance with different frequency control signals which are subject to abnormal absence but continue normally to recur alternately, comprising:

, (a) a plurality of parallel channels having a common input for receiving-all said control signals,

(b) a plurality of discrimination means respectively in said channels for efiectively assigning each channel a respective one of said control signals by discriminating against all said control signals except the said one which it passes as an output normally recurring in the same manner as the passed control signal,

(c) a plurality of switch means respectively coupled to said discriminating means,

((1) each said switch means having open and closed positions and being operated to one of said positions by the respective one of said discriminating means outputs, and

(e) means for coupling all said switch means to said device to cause said device to be operated at least temporarily if any of said switch means is in the other of its said positions.v

3. Apparatus including the said control circuit of claim 2, for use with the said control signals which are different frequency modulations on a carrier, and further comprising means for demodulating said carrier to provide said modulations to the said common input as said control generically related to that inthe copending McKee et al. signals.

4. A control circuit as in claim 2 wherein each said discrimination means includes a different filter which substantially passes to a common potential point only signals having frequencies substantially other than that of the respective said one control signal.

5. A circuit as in claim 2 wherein said switch means are coupled to said discrimination means by a respective emitter follower coupled at its input to the input of the respective said discrimination means, and by means for smoothing the output of each of said emitter followers.

6. A circuit as in claim 5 wherein each of said switching means is a respective relay the armatures of which are connected together.

7. A control circuit as in claim 5 including a respective diode between each of said discrimination means and a common potential point, said feedback means from the collector outputs of said emitter followers to the respective junctions between said discrimination means and diodes. I

8. A receiver including the control circuit of claim 2 and having means for receiving said control signals in modulated form and demodulating same to present them to said control circuit.

9. A system including the receiver of claim 8 and further including means for generating and transmitting thereto said recurrent control signals in modulated form. 10. A system including said control circuit of claim 2 and further comprising means for generating and transmitting a carrier signal, means for generating and modu lating first and second frequency control signals onto said carrier signal for transmission therewith alternately as aforesaid, and means coupled to said control circuit for receiving the so transmitted signal and demodulating same to present said control signals to said control circuit.

11. A system as in claim 10 including means for interrupting generation of said carrier signal during times when neither of saidcontrol signals is to be modulated thereon.

12. In apparatus for controlling a device in accordance with different frequency control signals which are subject to abnormal absence but continue normally to recur alternately, the improvement of a fail-safe control circuit comprising:

a plurality of parallel channels having a common input for receiving all said control signals,

a plurality of discrimination means respectively in said channels for effectively assigning each channel a respective one of said control signals by discriminating against all said control signals except the said one which it passes as an output normally recurring in the same manner as the passed control signal,

a plurality of switch means coupled at their inputs respectively to said discriminating means, and 7 means coupling the outputs of all said switch means together for common connection to said device,

each said switch means having open and closed positions one of which is normal and causes said device to be operated through said connection means,

each of said switch means being responsive to the respective one of said discriminating means outputs to operate itself into the other of said open and closed positions for preventing operation through said common connection means of said device only as long as there is a lack of abnormal absence that is a presence of either of said recurrent discriminating means outputs.

13. Apparatus as in claim 12 including said device, said device having means coupled to said control circuit by said common connection means for effecting a signalling indication only if either of said switch means. is abnormally in the said one position.

14. Apparatus as in claim 12 comprising a receiver including the said control circuit and having means for receiving said control signals in modulated form and demodulating same to present them to said control circuit.

15. Apparatus as in claim 14 and further including means for remotely generating and transmitting to said receiver the said recur-rent control signals in modulated form.

16. Apparatus as in claim 12 and further comprising:

means for generating and transmitting a carrier signal,

means for recurrently generating and modulating first and second frequency control signals onto said carrier signal for transmission therewith alternately as aforesaid, and

means coupled to said control circuit for receiving the so transmitted signals and demodulating same to present said control signals to said control circuit.

17. Apparatus as in claim 16 wherein at'certain times no one of said control signals is to be modulated onto said carrier signal, and including means for interrupting generation of said carrier signal during said certain times.

18. A fail-safe warning system for providing an alarm signal upon detection of an approaching train comprising:

a transmitter having means for generating spaced,

normally recurrent control signals which are subject to abnormal absence at least when said train approaches a warning device, and

a receiver disposed remotely from said transmitter for receiving said control signals to operate said warning device during the abnormal absence of said control signals,

said receiver including: I

multi-condition means connected at its output to said warning device and operative between two conditions, one of said conditions being normally stable and the other of said conditions being normally unstable, and

timing means responsive to receipt by said receiver of said control signals for causing said multi-condition means to be in said unstable condition and prevent operation of said warning device only so long as the time interval between certain ones of said control signals is no greater than a predetermined time as determined by the said timing means.

19. A warning system as in claim 18 where said control signals are substantially of a first frequency and where said receiver includes filter means for causing said timing means to be responsive to substantially only said first frequency.

20. A warning system as in claim 19 where said filter means is afilter which substantially passes to :a common potential only signals having frequencies substantially other than said first frequency.

21. A warning system as in claim 20 where said receiver includes an emitter follower coupled at its input to the input of said filter means and where said receiver includes a diode between said filter and a common potential point and feedback means from the collector output of said emitter follower to the junction between said filter and diode.

22. A warning systemas in claim 21 where said receiver includes means for smoothing the output of said emitter follower and Where said timing means includes a condenser coupled to the output of said smoothing means, and where said multi-condition means is a relay the coils of which are in circuit with said condenser.

23. A warning system as in claim 18 where said signal generating means is responsive to a continuous operation by an operator disposed at said transmitter and where said abnormal absence of said control signal occurs when said operator stops said continuous operation.

24. A warning system as in claim 18 where said transmitter includes modulator means for modulating said control signal upon a carrier signal and said receiver includes demodulator means for removing said control signal from said carrier signal.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Welker 317-149 X Undy 343--225 Wennemer 317147 X Polyzou et a1 317-138 X. Koehler 317-138 X Amfahr.

Chater.

Marks 329--103 Purington 343225 Tschumi et a1 317138 X Willard 317147 Schalkwijk 317138 Hooper 31714'7 SAMUEL BERNSTEIN, Primary Examiner.

LLOYD MCCOLLUM, Examiner. 10 L. T. HIX, Assistant Examiner. 

12. IN APPARATUS FOR CONTOLLING A DEVICE IN ACCORDANCE WITH DIFFERENT FREQUENCY CONTROL SIGNALS WHICH ARE SUBJECT TO ABNORMAL ABSENCE BUT CONTINUE NORMALLY TO RECUR ALTERNATELY, THE IMPROVEMENT OF A FAIL-SAFE CONTROL CIRCUIT COMPRISING: A PLURALITY OF PARALLEL CHANNELS HAVING A COMMON INPUT FOR RECEIVING ALL SAID CONTROL SIGNALS, A PLURALITY OF DISCRIMINATION MEANS RESPECTIVELY IN SAID CHANNELS FOR EFFECTIVELY ASSIGNING EACH CHANNEL A RESPECTIVE ONE OF SAID CONTROL SIGNALS BY DISCRIMINATING AGAINST ALL SAID CONTROL SIGNALS EXCEPT THE SAID ONE WHICH IS PASSES AS AN OUTPUT NORMALLY RECURRING IN THE SAME MANNER AS THE PASSED CONTROL SIGNAL, A PLURALITY OF SWITCH MEANS COUPLED AT THEIR INPUTS RESPECTIVELY TO SAID DISCRIMINATING MEANS, AND MEANS COUPLING THE OUTPUTS OF ALL SAID SWITCH MEANS TOGETHER FOR COMMON CONNECTION TO SAID DEVICE, EACH SAID SWITCH MEANS HAVING OPEN AND CLOSED POSITIONS ONE OF WHICH IS NORMAL AND CAUSES SAID DEVICE TO BE OPERATED THROUGH SAID CONNECTION MEANS, EACH OF SAID SWITCH MEANS BEING RESPONSIVE TO THE RESPECTIVE ONE OF SAID DISCRIMINATING MEANS OUTPUTS TO OPERATE ITSELF INTO THE OTHER OF SAID OPEN AND CLOSED POSITIONS FOR PREVENTING OPERATION THROUGH SAID COMMON CONNECTION MEANS OF SAID DEVICE ONLY AS LONG AS THERE IS A LACK OF ABNORMAL ABSENCE THAT IS A PRESENCE OF EITHER OF SAID RECURRENT DISCRIMINATING MEANS OUTPUTS. 